[Aavso-photometry] Re: Images of B and V filters.

[Stan Walker]

Richard,

Those were very interesting - or alarming - photos. I haven't been using my 
filters for a while but this encouraged me to pull the filters from the 
wheel and look at them. These are probably different, being designed for the 
ST6B. But there was no trace of this type of deterioration. There were some 
salt flecks on the V filter, which was in the light path, but these came off 
easily.

I'm unsure what the glasses are but they were designed by Mike Bessell and 
built at Mt Stromlo - so they're about 4 years old, I think. I'm located 
about 30 metres ASL and 100 metres from the east coast in a part of New 
Zealand where it's 6 kilometres from coast to coast. Plenty of humidity and 
in last week's storm the salt haze from the Tasman Sea was completely across 
the land here. The V filter has 3mm of a green glass and 1mm of yellow. The 
B filter is 1mm blue, 2mm blue-green and 1mm that looks clearish from the 
edge. Presumably these are similar to the glass types you quote?

Norman Walker seems to have one solution but Bessell doesn't seem to have 
had to go to these lengths. It's great seeing colour photometry done, but 
alarming if the filters are dubious. Richard - thanks for going to the 
trouble of sending these photos.

Regards,
Stan
----- Original Message ----- 
From: "Richard Miles" <rmiles.btee at btinternet.com>
To: "Stan Walker" <astroman at xtra.co.nz>; "arne" <arne at aavso.org>; "Michael 
Koppelman" <lolife at bitstream.net>
Sent: Wednesday, September 28, 2005 10:51 PM
Subject: Images of B and V filters.


> Guys,
>
> As promised.
>
> Richard
>